Extensive and detailed theoretical information about electronic structure is of fundamental importance to the interpretation of molecular conformation and spectroscopy. This proposal involves semiempirical molecular orbital calculations on a variety of organometallic systems which serve as model compounds for parts of the active sites in copper proteins. Copper-containing proteins such as plastocyanin, azurin, stellacyanin and superoxide dismutase all feature Cu(II) centers coordinated by one or more ligands featuring N or S donor atoms such as imidazole, imidazolate, thioether, and thiolate. Methodologies for reliable detailed predictions of the structural and spectroscopic properties in such complexes will be developed and insights into and explanations for the "blue" copper protein spectral features sought. Particular emphasis will be placed on investigating how the ground and excited state properties depend on and respond to conformational changes, ligand-metal and ligand-ligand interactions, alkylation of ligands, substitution of central metal ion, and the presence of counterions or solvent molecules. Some specific aims are: (a) Extensive study into the suitability and reliability of an INDO molecular orbital method for metalloorganic systems containing Cu(II); (b) detailed characterization of the LMCT spectra in Cu(II)- (and Ni(II)-) complexes containing imidazole, imidazolate, thioether, and thiolate; (c) development and implementation of special purpose utility routines for the calculation of parameters appropriate for ESR, Resonance Raman, CD, and MCD spectroscopy; and (d) systematic evaluation of calculated data obtained on well characterized model compounds leading to investigation of realistic models for the Cu(II)-site in plastocyanin, azurin, and perhaps stellacyanin. A reliable theoretical model with predictive power will provide a firm foundation for studies extending beyond the better characterized systems towards, for example, ligand identification in not fully characterized chromophores (e.g. stellacyanin), binuclear metal complexes (e.g. superoxide dismutase or "type 3" copper proteins), photochemistry of Cu-complexes, and Cu(II) binding sites in drugs (e.g. cimetidine, bacitracin, bleomycin).